Method and apparatus for performing distribution in a communication system

ABSTRACT

A switch (101) performs distribution functions by distributing packets to base stations that were most recently heard from. More particularly, as a gateway (115) provides frames to the switch (101), the switch (101) distributes the frames to all base stations in communication with a remote unit (113). In order to determine the plurality of base stations requiring the frames, an identification of base stations (on a per-call basis) currently backhauling data to the switch (101) for the call is maintained. The switch (101) then distributes frames received from the gateway (115) to those base stations currently providing uplink frames to the switch (101) for the particular call.

FIELD OF THE INVENTION

The present invention relates generally to wireless communicationsystems and in particular, to performing distribution within suchwireless communication systems.

BACKGROUND OF THE INVENTION

Selection and distribution within wireless communication systems isknown in the art. One such communication system employing selection anddistribution is a Code Division Multiple Access (CDMA) communicationsystem as described in Cellular System Remote unit-Base StationCompatibility Standard of the Electronic IndustryAssociation/Telecommunications Industry Association Interim Standard 95A(IS-95A/B), which is incorporated by reference herein. (EIA/TIA can becontacted at 2001 Pennsylvania Ave. NW Washington D.C. 20006). Asdescribed in IS-95A/B, as a remote unit moves to the edge of a cell, itmay commence communication with an adjacent base station, while thecurrent base station continues to handle the call. The call is thenhandled simultaneously by both base stations. During such a scenario,the remote unit is said to be in soft handoff Soft handoff providesdiversity of forward traffic channels and reverse channel paths on theboundaries between base stations. Each base station involved in aparticular soft handoff, demodulates the traffic channel frames andprovides the frames to a selector function. The selector function thenselects the best frame from each of the active call legs and that frameis forwarded on to the rest of the communication network. Likewise, thecommunication network provides frames to a distribution function thatare to be transmitted to the remote unit. The distribution functiondistributes these frames to all base stations involved in soft handoffwith the remote unit.

In current CDMA communication systems, to support soft handoff, allselection/distribution functions take place in software/hardwareentities (e.g., Mobile Switching Centers (MSCs), Centralized BaseStation Controllers (CBSCs), . . . , etc.) apart from base stationswithin the communication system. Base stations within prior-artcommunication systems are simply hard-wired to a single selection unitthat does not vary with time. While such a configuration is adequate forexisting CDMA communication systems, this configuration is inadequatefor next generation CDMA communication systems, since all nextgeneration CDMA systems virtually eliminate the need for MSCs and CBSCs.Therefore, a need exists for a method and apparatus for performingdistribution within a communication system that is capable ofaccommodating next generation CDMA communication systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a communication system in accordance withthe preferred embodiment of the present invention.

FIG. 2 is a block diagram of a base station of FIG. 1 in accordance withthe preferred embodiment of the present invention.

FIG. 3 is a flow chart illustrating operation of the base station ofFIG. 1 in accordance with the preferred embodiment of the presentinvention during a call origination.

FIG. 4 is a flow chart illustrating operation of the base station ofFIG. 1 during soft handoff in accordance with the preferred embodimentof the present invention.

FIG. 5 is a flow chart showing the selection of a call anchoring basestation in accordance with the preferred embodiment of the presentinvention.

FIG. 6 is a flow chart showing operation of the switch of FIG. 2 inaccordance with the preferred embodiment of the present invention.

FIG. 7 is a flow chart showing the operation of the selector of FIG. 2in accordance with the preferred embodiment of the present invention.

FIG. 8 is a flow chart showing operation of the frame-forwardingcircuitry of FIG. 2 in accordance with the preferred embodiment of thepresent invention.

FIG. 9 is a block diagram of the switch of FIG. 1 in accordance with thepreferred embodiment of the present invention.

FIG. 10 is a block diagram showing operation of the switch of FIG. 1 inaccordance with the preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

To address the need for distribution within a communication system, amethod and apparatus for performing distribution within a communicationsystem is provided herein. A switch performs distribution functions bydistributing packets to base stations that were most recently heardfrom. More particularly, as a gateway provides frames to the switch, theswitch distributes the frames to all base stations in communication witha remote unit. In order to determine the plurality of base stationsrequiring the frames, an identification of base stations (on a per-callbasis) currently backhauling data to the switch for the call ismaintained. The switch then distributes frames received from the gatewayto those base stations currently providing uplink frames to the switchfor the particular call.

The present invention encompasses a method for performing selectionwithin a communication system. The method comprises the steps ofidentifying a plurality of base stations currently providing uplink datafor a call to a switch, and receiving downlink data to be distributed tothe plurality of identified base stations. The downlink data isdistributed to the plurality of identified base stations based on thestep of identifying.

The present invention additionally encompasses a method for performingdistribution within a communication system. The method comprises thesteps of receiving, from a base station, a first packet that is to berouted to a selection function, determining a call identification and abase station identification from the first packet, and determining acurrent time. The call identification, a base station identification,and the current time is stored in a buffer. A second packet is receivedthat is to be distributed to a plurality of base stations involved in acall. The buffer is then analyzed to determine base stations existing onthe buffer identified with the call, and the second packet isdistributed to the base stations existing on the buffer identified withthe call.

The present invention additionally encompasses an apparatus forperforming distribution in a communication system. The apparatuscomprises a logic unit having a first packet received from a basestation as an input and outputting information based on the first packetreceived, a buffer having the output information as an input, and arouting function having a second packet as an input and an outputcomprising the second packet. In the preferred embodiment of the presentinvention the second packet is output to a plurality of base stationsdetermined based on a content of the buffer.

Turning now to the drawings, wherein like numerals designate likecomponents, FIG. 1 is a block diagram of communication system 100 inaccordance with the preferred embodiment of the present invention. Inthe preferred embodiment of the present invention, communication system100 utilizes a CDMA system protocol as described in IS-95A/B, but inalternate embodiments communication system 100 may utilize other analogor digital cellular communication system protocols that require amacro-diversity frame selection and distribution to take place.

Communication system 100 comprises base stations 103-109, each havingrespective coverage area 117-123, remote unit 113, backhaul 111, switch101, sidehaul 112, and gateway 115. In the preferred embodiment of thepresent invention base stations 103-109 are preferably Motorola, Inc.base stations that are configured with processors, memories, instructionsets, and the like, to function in any suitable manner to perform thefunction set forth herein. Additionally, in the preferred embodiment ofthe present invention, switch 101 comprises a packet switch (router)such as a Cisco Model MGX-8800 or other network access equipment. Ciscocan be contacted within the United States at 170 West Tasman Dr., SanJose, Calif. 95134. Backhaul 111 and sidehaul 112 comprise T1 span linesthat terminate at switch 101 and each base station 103-109, but inalternate embodiments of the present invention, backhaul 111 andsidehaul 112 may comprise other backhaul and sidehaul means such asOptical Connection 3 (OC3), fiber optic cable, . . . , etc. Finally,gateway 115 may connect communication system 100 to any service network,such as, but not limited to, a Public Switched Telephone Network (PSTN),an Integrated Switched Digital Network (ISDN), an InternationalTelecommunication's Union (ITU) H.323 network, a Wide Area Network(WAN), a Local Area Network (LAN), a digital subscriber line (DSL) or aninternet network.

As shown, remote unit 113 currently exists in coverage areas 117-121,and is in three way soft handoff with base stations 103-107. In thepreferred embodiment of the present invention, a single call anchoringbase station from base stations 103-107 is chosen to perform selection,and call processing functions for the particular call (i.e., act as acall anchoring base station for the particular call) based on astatistic, which in the preferred embodiment of the present invention isa work-load metric. The determination of the call anchoring base stationis made based on the base station with a lowest mean work load (in thisexample base station 103). During communication with remote unit 113,frames received by base stations 103-107 are assigned a frame-qualityindicator (FQI) by the base station. In the preferred embodiment of thepresent invention FQI is preferably quality bits from the forward errorcorrection (FEC) function that is used on the radio channel. The FECfunction may or may not involve an additional automatic repeat request(ARQ) on the link. Thresholds are configurable via operations andmaintenance processes or dynamically adjusted via optimizationalgorithms. In alternate embodiments of the present invention, otherFQIs may be utilized instead (e.g., Reed Solomon, BCH codes, Turbocodes, . . . , etc.)

For non-anchoring base stations 105-107 FQI information for all framesreceived is continuously backhauled to switch 101 via backhaul 111. Inparticular, base stations 105-107 continuously backhaul a FQI₋₋ SIDEHAULmessage containing base station identification, mean base station workload, call identification, and FQI. Switch 101 then sidehauls the FQIinformation to the call anchoring base station (in this case, basestation 103), where a determination of a base station with the best FQIfor each frame takes place.

Once the anchoring base station determines a base station with the bestFQI for a particular frame, the anchoring base station sends a FORWARD₋₋FRAME message to the base station with the best FQI, or, if theanchoring base station is the base station with the best FQI, nothing issent to the other base stations. The FORWARD₋₋ FRAME message comprises aframe number and a destination address. Once the FORWARD₋₋ FRAME messageis received by a base station, the base station immediately forwards theframe (identified by the frame number) to switch 101. In the preferredembodiment of the present invention the identified frame is transmittedin packet form with an address field comprising the destination address.Switch 101 then routes the selected frame to gateway 115, and ultimatelyto the destination address.

In the preferred embodiment of the present invention all framestransmitted to switch 101 is done so via a packet protocol such as anInternet Protocol (IP). However, other packet protocols may be utilizedinstead of IP (e.g., Frame Relay or Asynchronous Transfer Mode (ATM)). Avariety of voice/data compression formats may also be used over IPnetworks. Synchronization of the IP packets and pathway setup betweenbase stations is achieved using real time streaming protocol (RTSP) asdescribed in Internet Engineering Task Force (IETF) Request for Comment2326. CDMA soft hand over adds are handled as "an addition of a mediaserver (in our case a base station) to a conference" in RTSP parlance.Quality of Service (QoS) are maintained by using Resource ReservationProtocol (RSVP) an IETF draft standard. In the preferred embodiment ofthe present invention User Datagram Protocol (UDP) port numbers are usedto identify individual data/voice channels. A large variety of backhaulmultiplexing methods work with this method as one skilled in the art caneasily recognize.

The above-described method for selection results in nothing beingsidehauled except FQI bits for 1/3 of the time for a call in 3-way softhandoff assuming an equal distribution of poor quality frames. For 2/3of the time FORWARD₋₋ FRAME messages are being sidehauled. Assuming a22-byte full-rate voice frame with an 8-byte header, the sidehaulrequirements are approximately 1.41 times the channel capacity for acell with all dedicated remotely located selector functions.

FIG. 2 is a block diagram of a base station 103 of FIG. 1 in accordancewith the preferred embodiment of the present invention. Base station 103comprises antenna 201, transceiver 203, switch 204, delay circuitry 205,selector circuitry 207, controller 209, and frame-forwarding circuitry211. In the preferred embodiment of the present invention selectioncircuitry 207 comprises software/hardware that performs CDMA frameselection as described above. In other words, selector 207 determines abase station having a best FQI for a particular frame and instructs thatbase station to forward the frame to switch 101 by sending the FQI₋₋SIDEHAUL message. During operation of base station 103, controlcircuitry 209 determines if base station 103 will be performing selectorfunctions or not. As discussed above, the determination of the callanchoring base station is made based on the base station with a lowestmean work load, which is also exchanged in the METRIC SIDEHAUL messagein addition to the FQL₋₋ SIDEHAUL. The METRIC₋₋ SIDEHAUL bidding processmay be performed independently of the FQI bidding process.

During time periods when base station 103 is performing selection,frames received by transceiver 203 are output to switch 204. Controller209 instructs switch 204 to pass frames received from transceiver 203 todelay circuitry 205 and to selector 207. In the preferred embodiment ofthe present invention, delay circuitry 205 serves to delay frames for anamount of time so that frames from all base stations in soft handoffwith remote unit 113 enter selector 207 simultaneously. Selector 207determines an FQI for the received frame and receives FQI informationfor the frame from base stations in soft handoff with remote unit 113via the FQI₋₋ SIDEHAUL message. Selector 207 then selects the basestation with the best FQI from all base stations involved in softhandoff with remote unit 113. If the anchor base station (i.e., basestation 103) is the base station with the best FQI for the frame, thenthe anchor base station passes the frame to switch 101 (via IP packet).However, if the anchoring base station does not have the best FQI forthe frame, then a FORWARD₋₋ FRAME message is passed to the base stationhaving the best FQI for the frame.

During time periods when base station 103 is not performing selectionfunctions for a particular call (i.e., does not have the lowest meanwork load of all base stations in soft handoff with remote unit 113),controller 209 instructs switch 204 to pass all frames received fromtransceiver 203 to frame-forwarding circuitry 211, bypassing selector207. Frame-forwarding circuitry 211 determines FQI information forframes entering circuitry 211 and continuously sidehauls the FQIinformation to an anchor base station. When a FORWARD₋₋ FRAME message isreceived by circuitry 211, circuitry 211 forwards the frame identifiedin the message to gateway 115, and ultimately to a destination addressidentified in the message.

It should be noted that in the preferred embodiment of the presentinvention the decision of whether a base station is going to act as ananchor base station for a particular call is made on a call-by-callbasis. Therefore, for each remote unit in communication with a basestation, a determination is made as to which base station in softhandoff with the remote unit has the lowest work-load, and that basestation performs selection functions. For example, a particular basestation may be acting as an anchor base station for a first remote unit,yet may be acting as a non-anchor base station for a second remote unit.During such a situation, the particular base station will be receivingcommunication from both remote units, each in soft handoff with aparticular group of base stations. While acting as the call anchor, thebase station has the lowest mean work load for all base stations in softhandoff with the first remote unit, yet will not have the lowest meanwork load for base stations in soft handoff with the second remote unit.

FIG. 3 is a flow chart illustrating operation of the base station ofFIG. 1 during a call origination in accordance with the preferredembodiment of the present invention. In other words, FIG. 3 is a flowchart showing the operation of base station 103 during those timeperiods when remote unit 113 first accesses communication system 100. Atstep 301, base station 103 receives a message from remote unit 113, andat step 305, base station 103 determines if the message is a callorigination message. If, at step 305, base station 103 determines thatremote unit 113 has sent a call origination message, then the logic flowcontinues to step 310 where base station 103 assigns remote unit 113 atraffic channel and begins communication with remote unit 113 via thetraffic channel. At step 315, base station 103 receives transmissionsfrom remote unit 113 and acts as the default anchor for the call,routing all frames to switch 101. Thus, in the preferred embodiment ofthe present invention during all call originations, the base stationreceiving the call origination will automatically default to performinganchor functionality until soft handoff legs are added to the call.Returning to step 305, if base station 103 determines that the messagesent from remote unit 113 is not a call origination message, then thelogic flow continues to step 320, where normal messaging takes place(e.g., pages, page responses, registrations, . . . , etc.) betweenremote unit 113 and base station 103. The logic flow then returns tostep 301.

FIG. 4 is a flow chart illustrating operation of base station 103 inaccordance with the preferred embodiment of the present invention duringsoft handoff. The logic flow begins at step 401 where remote unit 113has successfully originated a call, and is communicating with basestation 103. As described above with reference to FIG. 3, base station103 is performing anchor functionality until soft handoff legs are addedto the call. At step 403, controller 209 determines if a soft handoffleg should be added to the call. This is accomplished by controlcircuitry 209 receiving a signal strength measurement (IS-95A/B PilotStrength Measurement Message (PSMM) of a neighboring base station anddetermines if the PSMM is greater than a threshold (IS-95A/B T₋₋ ADD).If at step 403, it is determined that a soft handoff leg should be addedto the current call, then the logic flow continues to step 405 where ahandover request message is routed to the target base station (e.g.,base station 105). In the preferred embodiment of the present inventionthe handover request message is routed from control circuitry 209through switch 101, and finally to target base station 105.

At step 407 a determination is made as to which base station (i.e., basestation 103 or base station 105) should serve as the call anchoring basestation. As discussed above, the call anchoring base station is chosenbased on the current work load for each base station, and the basestation having the lowest mean work load is chosen to perform anchorfunctionality. Next, at step 409, controller 209 determines if an anchorhandover is necessary. In other words, controller 209 determines if basestation 105 should be performing anchor functionality for the particularcall (i.e., selection and call processing/control). If at step 409 it isdetermined that an anchor handover is necessary, then the logic flowcontinues to step 411 where an anchor handoff is performed, and basestation 105 begins performing anchor functionality for the particularcall and the logic flow returns to step 403. However, if at step 409, itis determined that an anchor handoff is not necessary, then at step 413base station 103 continues performing anchor functionality (i.e.,selection and call processing/control) and the logic flow returns tostep 403.

FIG. 5 is a flow chart showing the selection of a call anchoring basestation in accordance with the preferred embodiment of the presentinvention (step 407 of FIG. 4). The logic flow begins at step 501 wherecontroller 209 determines the current work load for the current callanchoring base station (i.e., base station 103). In the preferredembodiment of the present invention the current work load is defined asbeing the current backhaul utilization for the call anchoring basestation, however other work-load functions may be utilized as well.Next, at step 503, a current work load for base stations in soft handoffis determined. In the preferred embodiment of the present invention thisis accomplished by the call anchoring base station receiving periodicupdates of the work load for all base stations within the active setalong with sidehauled frame information (i.e., within the FQI₋₋ SIDEHAULmessage). Thus, those base stations that are not acting as a callanchoring base station for the particular call, will periodicallydeliver a work load metric to the call anchoring base station along withthe FQI sent to the call anchoring base station.

In alternate embodiments of the present invention, other forms ofdetermining the current work load for base stations within the activeset are envisioned. For example, all base stations currently in softhandover with remote unit 113 (i.e., all base stations within theIS-95A/B active set) can be sent a request to provide the current callanchoring base station with a current work load metric. This may takeplace by transmitting a control message to all base stations within theIS-95A/B active set via switch 101 in accordance with standard switchingtechniques.

Continuing, at step 505 a current work load is determined for thecandidate base station (i.e., base station for which soft handover isrequested). Finally, at step 507 a base station having the lowest workload is determined. For example, if the current call anchoring basestation is utilizing 80% of its backhaul capacity, and a anchorcandidate base station is utilizing 50% of its backhaul capacity, thenthe anchor candidate base station has a lower work load than the currentcall anchoring base station. The logic flow continues to step 409 (FIG.4).

FIG. 6 is a flow chart showing operation of the switch of FIG. 2 inaccordance with the preferred embodiment of the present invention. Thelogic flow begins at step 601 where a frame is output from transceiver203 to switch 204. Next, at step 603 controller 209 determines if thebase station is operating as an anchor base station. If at step 603 itis determined that the base station is an anchor base station, then thelogic flow continues to step 605 where switch 204 passes the frame toselector 207, otherwise the logic flow continues to step 607 whereswitch 204 passes the frame to frame forwarding circuitry 211.

FIG. 7 is a flow chart showing the operation of selector 207 inaccordance with the preferred embodiment of the present invention. Thelogic flow begins at step 701 where selector 207 receives a frame(received from transceiver 203) from a particular call from switch 204.Additionally, at step 701, selector 207 receives second and third FQIfrom all base stations in soft handoff with the particular call via theFQI₋₋ SIDEHAUL message. As discussed above, FQI information from a basestation indicates the quality of a particular frame that was received bythe base station. By receiving FQI information from all base stations insoft handoff with the remote unit, selector 207 receives information onhow well each base station in soft handoff with the remote unit receivedthe frame.

Continuing, at step 703, selector 207 determines first FQI for the framereceived from switch 204. At step 705 selector 207 determines a basestation that has the best FQI for the frame. At step 707 selector 207compares the best FQI to a threshold and determines if the best FQI isabove a threshold. In the preferred embodiment of the present inventionit is anticipated that situations arise where all frames received by thebase stations in soft handoff with a remote unit will have a poor FQI.In these situations it is desirable to have no frame passed to switch101 (provided it is not needed). Therefore, if at step 707, selector 207determines that the best FQI is not above the threshold, then the logicflow simply returns to step 701, with no frame being passed to switch101. However, if at step 707 it is determined that the best FQI is abovethe threshold, then the logic flow continues to step 709 where selectordetermines if the first FQI (received by the anchor base station) is thebest FQI and if so, the logic flow continues to step 711 where the framereceived by selector 207 is passed (in packet form) to switch 101. If,however, it is determined that the best FQI is not the first FQI, thenthe logic flow continues to step 713 where a FORWARD₋₋ FRAME message istransmitted to the base station having the best FQI.

FIG. 8 is a flow chart showing operation of the frame-forwardingcircuitry of FIG. 2 in accordance with the preferred embodiment of thepresent invention. The logic flow begins at step 801 whereframe-forwarding circuitry 211 receives a frame (received fromtransceiver 203) from a particular call from switch 204. Next, at step803 frame-forwarding circuitry 211 determines if a FORWARD₋₋ FRAMEmessage has been received indicating that the frame for the particularcall should be forwarded to switch 101. If at step 803 it is determinedthat a FORWARD₋₋ FRAME message has been received, then the logic flowcontinues to step 805 where the message is analyzed to determine addressinformation, and at step 807 the frame is forwarded to the addressindicated in the FORWARD₋₋ FRAME message.

Returning to step 803, if it is determined that a FORWARD₋₋ FRAMEmessage has not been received, then the logic flow continues to step 809where an FQI is determined for the frame. Next, at step 811 the FQI istransmitted to the anchoring base station.

FIG. 9 is a block diagram of the switch of FIG. 1 in accordance with thepreferred embodiment of the present invention. In the preferredembodiment of the present invention switch 101 performs distributionfunctions by distributing packets to base stations that were mostrecently heard from. More particularly, as gateway 115 provides framesto switch 101, switch 101 distributes the frames to all base stations incommunication with remote unit 113. In order to determine the pluralityof base stations requiring the frames, an identification of basestations (on a per-call basis) currently backhauling data to switch 101for the call is maintained. Switch 101 then distributes frames receivedfrom gateway 115 to those base stations currently providing uplinkframes to switch 101 for the particular call. Unlike prior-art methodsof distribution, in the preferred embodiment of the present inventionbase stations involved in a particular call do not need to identifythemselves. Switch 101 "remembers" the base stations providing uplinkframes for an identified call, and distributes downlink frames for thecall to those base stations. Switch 101 comprises logic unit 905, buffer907, timer 909, and routing function 911. Operation of switch 101 inaccordance with the preferred embodiment of the present invention occursas described in FIG. 10.

The logic flow begins at step 1001 where packets from base stations incommunication with remote unit 113 are received. As described above,during communication with remote unit 113, frames received from remoteunit 113 by base stations 103-107 are assigned a frame-quality indicator(FQI) by the base stations. For non-anchoring base stations 105-107 anFQI for the frames received is continuously backhauled to switch 101 viathe FQI₋₋ SIDEHAUL message. Additionally, once the anchoring basestation determines a base station with the best FQI for a particularframe, the anchoring base station sends a FORWARD₋₋ FRAME message toswitch 101, to be routed to the base station with the best FQI. At step1003 logic unit 905 determines if messaging has been received from abase station. In the preferred embodiment of the present invention logicunit 905 determines if either a FORWARD₋₋ FRAME message or a FQI₋₋SIDEHAUL message has been received by switch 101, however, in alternateembodiments of the present invention, other messages may be utilizedwithout varying from the scope of the invention. If a message has beenreceived by switch 101 an entry in buffer 907 is made (step 1005). Inparticular, at step 1005 logic unit 905 enters the base callidentification, station identification, and time for the particularmessage within buffer 907. The logic flow continues to step 1007. If, atstep 1003, it is determined that neither a FORWARD₋₋ FRAME message or aFQI₋₋ SIDEHAUL message has been received by switch 101, then the logicflow simply continues to step 1007. At step 1007 logic unit 905determines a current time and eliminates those entries from buffer 907that have been existing on buffer 907 for greater than a predeterminedamount of time (e.g., 140 ms (alternatively based on networkconditions)). In particular, logic unit 905 determines the time storedon buffer 907 for the particular entry, compares the time stored with acurrent time, and erases all entries older than a predetermined age.

At step 1009 logic unit 905 receives downlink packets for distributionand determines a call identification for the packet. At step 1011, logicunit 905 checks the contents of buffer 907 to determine all of theentries corresponding to the particular call identification. In otherwords, at step 1011 logic unit 905 identifies a plurality of basestations currently providing uplink data for an identified call. At step1013, logic unit 905 routes the packets to routing function 911 fordistribution to those identified base stations existing on buffer 907,having a similar call identification (i.e., in soft handoff with asimilar remote unit). The logic flow then returns to step 1001.

While the invention has been particularly shown and described withreference to a particular embodiment, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention.For example, although selection functionality takes place within a basestation, one of ordinary skill in the art will recognize that selectionin accordance with the preferred embodiment of the present invention mayoccur in other network elements (e.g., switch 101) without varying fromthe scope of the invention. In the situation where other networkelements are performing selection, all base stations will forward FQIbits to the network element, and that the network element will transmitFORWARD₋₋ FRAME messages to base stations having the best FQI. It isintended that such changes come within the scope of the followingclaims.

What is claimed is:
 1. A method for identifying base stations fordistribution of downlink data within a communication system, the methodcomprising the steps of:receiving, from a base station, a first packetthat is to be routed to a selection function; determining a callidentification and a base station identification from the first packet;determining a current time the first packet was received; storing thecall identification, the base station identification, and the currenttime the first packet was received in a buffer; receiving a secondpacket that is to be distributed to a plurality of base stationsinvolved in a call; analyzing the buffer to determine base stationsexisting on the buffer identified with the call; and distributing thesecond packet to the base stations existing on the buffer identifiedwith the call wherein base stations existing on the buffer are those whohave transmitted packets to the distribution function within apredetermined time period.
 2. The method of claim 1 wherein the step ofreceiving, from the base station, the first packet comprises the step ofreceiving, from the base station a first backhauled packet.
 3. Themethod of claim 1 further comprising the step of eliminating basestations from the buffer that have been existing on the buffer forgreater than a predetermined amount of time.
 4. An apparatus forperforming distribution in a communication system, the apparatuscomprising:a logic unit having a first packet received from a basestation as an input and outputting a call identification, a base stationidentification from the first packet, and a time the first packet wasreceived; a buffer storing the call identification, base stationidentification from the first packet, and the time the first packet wasreceived; and a routing function having a second packet as an input andan output comprising the second packet, wherein the second packet isoutput to a plurality of base stations that are determined based on acontent of the buffer wherein base stations existing on the buffer arethose who have transmitted packets to the distribution function within apredetermined time period.
 5. The apparatus of claim 4 wherein thereceived first packet comprises a packet that is to be routed to aselection function.
 6. The apparatus of claim 4 wherein the secondpacket comprises a packet that is to be distributed to a plurality ofbase stations in soft handoff with a call.
 7. The apparatus of claim 4wherein the plurality of base stations are in soft handoff with a remoteunit.
 8. The apparatus of claim 4 wherein the first packet is abackhauled packet.